Communication networks for voice communication, data links for computer systems, as well as remote sensing and control systems, often require that communication lines linking various nodes of the system be drawn through extensive lengths of conduit between the nodes. The conduit defines a path for the communication network and may be buried underground or may be positioned throughout a building or other structure. Access to the conduit is typically afforded only at isolated points where connections are made to system nodes. The conduit often has one or more bends as sharp as 90° which the communication lines must negotiate, as well as horizontal, vertical and angled segments of various lengths. Obstructions, in the form of other communication lines, are also often present within the conduit.
The communication lines to be drawn through the conduit may include, for example, simple wires, wiring harnesses, coaxial cable or optical fiber bundles. Other elongated items such as flexible sleeves for protecting the communication lines are also drawn through the conduit. Such protective sleeves often have pull cords pre-positioned within them for later drawing communication lines though the sleeve. As these lines and sleeves cannot be pushed through the conduit, it is found advantageous to draw them through the conduit by first drawing a high-strength pull cord in the form of a tape through the conduit, attaching the tape to the item to be drawn through the conduit, and drawing the item by pulling the tape.
The tape may be pneumatically drawn through the conduit by attaching it to a small parachute-like drogue, positioning the drogue within the conduit and forcing compressed air into the conduit behind the drogue. The drogue is inflated by the compressed air, preferably so that it fills the conduit. The differential pressure within the conduit which results from the inflated drogue will drive it through the conduit, the drogue drawing the pull tape along with it.
Unfortunately, parachute-like drogues, being fabric membranes, often collapse when negotiating bends such as elbow joints or obstacles within the conduit. Once collapsed, the differential pressure is lost and forward progress of the drogue, and its tape are halted. It can be very difficult to re-inflate a drogue which deflates deep within the conduit. The drogue must be drawn back to its starting point, re-inflated and another attempt made to negotiate the conduit. This process may be repeated many times before success is achieved, if at all. There is clearly a need for a device which can reliably negotiate conduit having bends and obstacles for positioning communication lines, as well as other elongated items such as protective sleeves.